Cellulosic structure and method for producing same



PatentedNov. 12, 1940 onnwnosrc srnuoruan AND METHOD roa raonucmo sane Franklin Traviss Peterawilmington, Del., auizm or to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing.

11 Claims.

I This invention relates to cellulosic structures,

especially those of pellicular nature. More particularly, it relates to a method for producing flexible and durable cellulosic pellicles by treating the same with softening agents, and the products resulting from such treatment.

In the manufacture of cellulosic pellicles of the type precipitated from aqueous alkaline cellulosic solutions, such as regenerated cellulose pellicles, including sheets or films, caps, bands, continuous tubing, artificial straw and the like, it has long been customary to incorporate into the cellulose pellicle a softening agent in order to maintain it in a flexible condition. Such cellulosic pellicles, when free from a softening agent, are known to be quite brittle, and while a softener-free pellicle may find certain uses, a softened and therefore fiexible sheet or film is much more generally useful. Heretofore, as softeners for regenerated cellulose, and similar water-sensitive cellulosic pellicles. the art has applied such substances as ethylene glycol, propylene glycol, diethylene glycol, foramide, glycerol, and the like, but of these, by far the most important is glycerol which has hitherto known no equal as a softening agent of general utility for producing flexible, transparent, and durable water-sensitive cellulosic pellicles such as those of regenerated cellulose. Many attempts have been made to find a softener for water-sensitive cellulosic pellicles which will'be as cheapas and which will have the generally useful softening characteristics of glycerol. After continued use of previously discovered softening agents they F were found to be deficient in some respect and therefore could not be generally substituted for glycerol as a softening agent for regenerated cel-.

lulose and like water-sensitive cellulosic pellicles.

Glycerol is obtained commercially primarily as a by-product from-the soap industry. As a byproduct, the quantity may be limited and hence glycerol is subject to market fluctuations of supply as well as price. Glycerol has-been particuperiods of war when large quantities are used in larly high-priced and diilicultly obtainable during less expensive equivalents ormeans for reducing Application May 9, 1939, Serial No. 272,640

the consumption of expensive materials will mean a marked economy in production.

It is, thereiore, an object of this invention to provide a new and useful method for producing softener water-sensitive cellulosic materials pos- 5 sessing desirable physical properties. It is a further object of this invention to provide watersensitive cellulosic materials having a softening agent associated therewith, which softening agent will not interfere with any subsequent treatment of the cellulosic pellicles, such as the application of surface coatings, ink, coloring matter, adhesives, or the like. It is a still further object of this invention to provide a rigid, flexible, transparent, durable, cellulosic pellicle, such as asheet, film or tube of regenerated cellulose in which the softening agent consists in whole or in part of a water soluble ammonium or substituted ammo nium salt of a low molecular weight aliphatic sulfonic acid. Other objects of the invention will appear hereinafter.

By the term "rigidity or its equivalent as used herein is meant that property which is the opposite of limpness; in other words, rigidity in the sense that the pellicle can be advanced in a wrapping machine or similar apparatus without curiing, crumpling or otherwise fouling the machine.

The term durability" is used to define resistance to shock or rough handling. Thus, for example, bags may be fabricated from the pellicle and filled with some standard material such as a certain weight of dried beans, and'the package sealed, whereupon the durability may be measured against a known standard by dropping the package under standard conditions and noting the resistance of the wrapper to breakage. v

The objects of this invention can be attained, in general, by treating a regenerated cellulose pellicle, or a like water sensitive, cellulosic pellicle,

with a softeningagent comprising a sulfonate of the following structure:

R1 R-SO:-NHR:

or more specifically,

O H, RI R-- 0-I IR:

in which R designates an alkyl or alkylol group containing 1 to 3 carbon atoms, and R1, R2, and R: designate a hydrogen ora beta-hydroxyethyl group. As specific examples of such compounds 5 may be mentioned ammonium propyl sulfonate, ammonium ethyl sulfonate, ammonium isopropyl sulfonate, diethanol ammonium ethyl, sulfonate, ethanol ammonium propyl sulfonate, ethanol ammonium isopropyl sulfonate, trlethanol ammonium ethyl sulfonate, ethanolamine gamma-hydroxypropyl sulfonate, ethanolamine beta-hydroiwpropyl sulfonate, and ammonium isethionate. The excess softening agent is then removed from thepellicle, and the pellicle so treated is dried. 1

In the manufacture of regenerated cellulose sheets or films, as for example by the'viscose process, the cellulosic dispersion is formed into a sheet or film by passing the same through suitable apparatus into coagulating and/or regenerating baths from which it is finally obtained in the form of a continuous cellulosic sheet which is customarily led in a continuous manner through a series of purifying, bleaching and washing operations. Just priorto the drying operation which is also usually continuous, coordinating with the sheet forming and purification operations, the film is passed through a bath containing a softening agent in such concentration that after the excess liquid has been removed from the surface of the sheet by suitable squeeze rolls and the excess moisture removed by passage through the dryer, the final sheet can be wound up in a con-' tinuous fashion and will contain an appropriate predetermined amount of softening agent.

The commercially available dry regenerated cellulose film contains approximately 4 to 8% moisture. Depending upon the particular uses for which the product is destined, the softening agent in the sheet or film, usually glycerol, may vary from about 8 to 25%, based on the combined weight of the cellulose and softening agent in the sheet.

The total amount of softener in the film'is controlled primarily by the total amount of softening agent in the treating bath; film thickness, rate of passage through the bath, temperature of the bath, etc., may also contribute thereto to a certain extent. The regenerated cellulose pellicle, when reaching the treating bath, is in a highly swollen and hydrated condition and usually the cellulose of the pellicle is associated with 300% or more of water. This highly swollen and wet pellicle, usually referred to as the gel sheet, is impregnated with the treating bath. Because of the large amount of water associated with the cellulose, it is apparent that the removal of this water during the drying operation will concentrate the softening agent with respect to the cellulose content of the pellicle.

Thus it is that if a regenerated cellulose pellicle containing about 15% total softener is desired as a final product, the concentration of softener in the treating bath will be adjusted to approximately one-third that value, or about 5%. This is true when the softening agents are, like glyc-' erol and the improved agents of this invention, substantiallynon-volatile and are not vaporized during the drying operation. It is obvious that if a mixed softener is used, the components of which are appreciably volatile during the drying operation, then the softener concentration of the treating bath must be increased sufficiently to compensate for the loss thereof during the drying step.

It has now been discovered that salts of the type indicated above are extremely well suited as softening agents for water-sensitive cellulosic pellicles, that is, pellicles produced from aqueous Water menses? alkaline cellulosic solutions or dispersions coagulated in an acid coagulating bath, especially those of regenerated cellulose, and that they may be used as substitutes for glycerol in this capacity. Furthermore, pellicles of regenerated cellulose softened with the materials of this invention possess desirable properties which are not found in similar pellicles in which the sole fiexibilizing and softening agent is glycerol.

The following examples will illustrate the practice of the invention, but it is to be understood that they are in no way limitative of the principles of the invention:

Example I A sheet or film of gel regenerated cellulose in which the final dry thickness will be about .0009" is immersed in or drawn through an aqueous bath containing ammonium propyl sulfonate in such concentration that the final dried product will contain about 6.3% moisture, and 16.5% of ammonium propyl sulfonate, based on the combined weight of cellulose and softener in the film. The sheet or film is allowed to remain in contact with the bath until thoroughly impregnated, whereupon it is removed from the bath, the excess liquid drained off or removed by suitable squeeze rolls, blotters, or the like, when the film can be dried in the usual manner down to the final moisture content indicated above. When tested at a relative humidity of about 35% at 24 C., or even at relative humidities as low as 15-22% at ordinary temperatures, the durability of the film is found to be at least equal to that of a similar regenerated cellulose film softened wlthabout 14% glycerol.

Example II A sheet or continuous film of gel regenerated cellulose such that the final dry thickness will be about 0.0012" is treated in the manner described in Example I, using, however, a treating bath having a composition capable of providing a final film containing about 6.3% moisture and 18% of ammonium ethyl sulfonate. In this case,

the final product will'be equal to or better than a a similar regenerated cellulosesheet or film bearing 15% to 16% glycerol as softener insofar as its physicalproperties are concerned, including transparency, flexibility, durability under varying conditions, and resistance to the propagation of fiame.

In a similar manner, the following baths may be used in treating gel regenerated cellulose: J

Example III Per cent by weight Per cent by weight Ethanol ammonium isopropyl sulfonate 6. 0

Ammonium isopropyl sulfonate 6.0 Water 94.0

Example IV Per cent by weight Diethanol ammonium ethyl sulfonate- 5.5 Water 94. 5

Example V l Per cent by weight Ethanol ammonium propyl sulfonate 6. 0 Water 94.0

Example VI Example VII Per cent by weight 'Iriethanol ammonium ethyl sulfonate-- 5.5 Water 94..

Example VIII Per cent by weight Ethanolamine hydroxy propyl sulfonate Water 93. 75

Sheets or films of gel regenerated cellulose treated with any of the baths described in Examples III to IX, inclusive, in'accordance with the procedure outlined in Example I, will show physical characteristics substantially equal to those of a similar regenerated cellulose sheet treated with a softener bath containing 4% to 5% of glycerol (that is, a final film containing about glycerol), especially when the physical properties include transparency, flexibility, rigidity, durability, surface slip, and the like.

The following example illustrates a method which may be employed when a relatively volatile cellulose softener is admixed with an alkyl sulfonate of the type described, and compensation is made for' loss during the drying operation:

Example X A sheet or continuous film of gel regenerated cellulose such that the final dry thickness will be about 0.0009" is immersed in or passed through a treating bath of the follcwing'approximate composition:

. Per cent by weight Diethanol ammonium ethyl sulfonate 2.75

Ethylene glycol 2.75 Water 94.5

In this bath, the ratio of dletanol ammonium ethyl sulfonate to ethylene glycol is about 1:1.

The film is treated as described in Example I with a surface coating which may be of any type I desired. Thus, for example, it may be provided with a moistureproofing coating which may contain a cellulose derivative, a plasticizer, a resin or blending agent and a moistureproofing agent, such as a wax or wax-like material. Surface coating in this case serves the double purpose of providing a moistureproof product and of preventing loss by evaporation of the relatively volatile ethylene glycol. Even when tested under such drastic conditions as described in Example I, the product istransparenhfiexible, and as durable as film softened with 15% glycerol.

Films obtained in the preceding examples are found to possess, in addition to good transparency, rigidity, fiexibility, durability, and excellent surface characteristics.

It is obvious that. in the above examples the concentration of 'total softening agent inthe treating bath may be suitably varied according to the base being treated in order that the final product will have the appropriate amount of softener.

As a base, the invention contemplates the use of any water-sensitive cellulosic structure, particularly of pellicular nature such as a sheet or film, artificial straw, caps, bands, or continuous tubes, such as may be obtained by the coagus lation and/or regeneration from an aqueous cellulosic dispersion in accordance with the procedure customary to the art; Thus, the invention comprehends the use of regenerated cellulose pelllcles such as may be obtained from the viscose or cuprammonium processes, as well as pelllcles composed of glycol cellulose, cellulose glycollic acid, lowly esterified or lowly etherified cellulose derivatives where there is only one ether or ester group associated with several cellulose units, and other cellulosic structures of similar character.

Similarly, various types of paper, especially of the glassine type, may be used as base ma terials. As a matter of convenience, the invention has been described in terms of its application to the softening of regenerated cellulose pelllcles such as those sheets or films of regenerated cellulose which are suitable for use as wrapping tissue, it being understood that the ,scope of the invention includes any of the other bases set forth above and that the invention is equally applicable thereto.

All of the examples given have been set forth in terms of a sheet or film of gel regenerated cellulose (gel regenerated cellulose being defined as a. water-swollen regenerated cellulose which has never been dried-hence that product which is obtained from the wet end of the casting machine). Obviously, this is the more practical way of practicing the invention, since the an already dried regenerated cellulose film with a softener of the character described, it is possible to rewet the dried film so as to render it highly swollen, whereupon it may be treated with treating baths similar to those described, but of composition suitable for obtaining the final prod- -uct desired. In the same way, any of the sheets set forth as equivalent to regenerated cellulose sheets can be substituted in the specific examples.

The invention has been described in part in terms of the use of glycerol in combination with the ammonium and alkyl ammonium salts of sulfonic acids. It is to be understood that other similar known cellulose softeners may be substituted for the glycerol and among those may be mentioned ethylene glycol, diethylene glycol, triethylene glycol, formamide, carbamide, and other substances known to the art as softeners for water-sensitive cellulose structures.

It is also tobe understood that various mixtures of the newly described softening agents v may be employed'with single softeners of the prior art or with mixtures of the latter, depending upon the type of finalfilm desired and the purposes for which the film is to be used.

If a colored cellulosic pellicle is desired, it may be obtained in any of the ways commonly known in the art, including the passage of the sheetor film through a bath containing a suitable dyestull. If desired, the dyestufl may be added to the bath used for intrdoucing .the softening agent. In the same way, after the film has been treated with the softening agent, it may subjected to any of the customary after-treatments such as sizing or coating, or the like, which may be customarily given to cellulosic pellicles of the type described, in just the same manner that 11, glycerol softened regenerated cellulose film, for example, may be treated. p The instant invention offers numerous advantages over-the prior art means of softening cellulosic pellicles of the type described. Since the v softening agents of the present invention are substantially solidsubstances at ordinary temperatures, the control of concentrations used for treating baths is greatly'simplifled. Because of characterlstics, particularly improved transpar-- ency, flexibility, durability, surface slip and the like. Since the softeners of this invention are not decrease over a period of time due to the loss of softener. Furthermore, sheets so softened may be employed at relatively high temperatures without undue loss by vaporization of the softener. These materials, being crystalline in character, can be obtained in the very pure state by the usual methods of crystallization. However, even though they may be purified by-crystalllzation, it

is found that they do not crystallize in the sheet, causing hazinesses many other salts are known to do.

Since these materials are insoluble in the: usual organic solvents, sheets softened therewith are suitable for the wrapping or insulating of materials such as oils, greases, and other materials with solvent action of the nature of organic solvents. a

Since it is obvious that many changes and mod ifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited thereto except as set forth in the following claims.

I claim:

1. A flexible, durable water-sensitive cellulosic structure of the type precipitated from aqueous alkaline cellulosic solutions, said structure containing, as a softener therefor, a sulfonate having the structure 60 7 R1 R-SOs-NHR! Ra in which R designates a. member of the group 5 consisting of alkyl and alkylol groups containing 1 to 3 carbon atoms, and R1, R2 and Rs designate menses g non-volatile, the softening action in the film does a member of the group consisting and beta-hydroxyethyl groups.

2. A flexible. durable regenerated cellulose structure of the type precipitated from aqueous alkaline cellulosic solutions, said structure containing. as a softener therefor, a sulfonate having the structure R: in which R designates a member of the group consisting of alkyl and alkylol groups containing 1 to 3 carbon atoms, and R1. R2 and Rs designate a. member of the group consisting of hydrogen and beta-hydroxyethyl groups.

3. A flexible, durable water-sensitive cellulosic structure of the type precipitated from aqueous alkaline cellulosic solutions," said structure containing, as a softener therefor, ammonium propyl sulfonate.

4. A flexible, durable water-sensitive cellulosic structure of the type precipitated from aqueous alkaline cellulose solutions, said structure containing. as a softener therefor, ammonium ethyl sulfonate. l

'5. A flexible, durable water-sensitive cellulosic structure of the type precipitated from aqueous alkaline cellulosic solutions, said structure containing, as a softener therefor, ammonium isopropyl sulfonate.

6. A flexible, durable water-sensitive cellulosic of hydrogen lei-sorstructure of the type precipitated from aqueous alkaline cellulosic solutions, said structure con taining. as a softener therefor, an ammonium alkyl sulfonate, said alkyl group containing 1' to 3 carbon atoms.

7. A regenerated cellulose pellicle softened with a sulfonate of theformula:

in which n is a positive integer not greater than 3. 9. A regenerated cellulose pellicle softened with ammonium ethyl sulfonate.

10. A regenerated cellulose pellicle softened with 8%25% ammonium ethyl sulfonate. 11. A water-sensitive cellulose film obtained by regeneration from an aqueous cellulosic dispersion softened with 8%-25% of ammonium ethyl sulfonate.

FRANKIJN TRAVISS PETERS. 

